This circuit was obtained from 1967 documentation. It uses a sensor to determine the trigger point. The components are of the time, difficulty to obtain these days.
This circuit produces a tone by a small loudspeaker. Frequency depends on C1 and C2. These...
We found this circuit in an 80's EDN. The circuit makes use of a MAX680, being given a table with...
Decade counters, such as the 4017, can be cascaded as sourcing signals with the frequency divided...